1. Field of the Invention
The present invention relates to an analog television (TV) broadcast signal receiver for receiving analog television broadcast signals such as NTSC (National Television System Committee).
2. Description of the Related Art
Currently in the North American Continent, NTSC (National Television System Committee) analog television broadcast (hereafter referred to simply as “analog TV broadcast”) and ATSC (Advanced Television Systems Committee) digital television broadcast (hereafter referred to simply as “digital TV broadcast”) coexist. Thus, there are a television receiver capable of receiving analog TV broadcasts (hereafter referred to as “analog TV receiver”) and a television receiver capable of receiving digital TV broadcasts (hereafter referred to as “digital TV receiver”). In the current situation where the analog and digital TV broadcasts coexist, a general TV broadcast receiver is already capable of receiving both TV broadcasts. Thus, unless otherwise stated, the term “TV receiver” is used in the present specification to mean a TV receiver capable of receiving both TV broadcasts.
When a user purchases a TV receiver, the user is required to register channels, which the user wishes to view, before the initial viewing. This is because a receiving direction of an antenna to give good received images varies with each channel. Particularly in the North American Continent, big cities spread across the plains. From the viewpoint of each TV user or viewer, TV broadcast signals come from various directions. Thus, it is necessary for the TV user to set the TV receiver so that the TV receiver stores receiving directions to give good received images for channels to view by associating the receiving directions with the channels.
For this reason, multi-directional antennas capable of changing receiving directions, such as a so-called smart antenna, are put to practical use. The EIA (Electronic Industries Association)-909 standard provides a smart antenna having sixteen equiangular receiving directions in 360 degrees omni-directionally. A TV receiver conforming to the EIA-909 standard is set to be able to adjust or change an active receiving direction of the multi-directional antenna such as the smart antenna to every one of the sixteen receiving directions.
Some of such TV broadcast receivers have an automatic scanning function to select and register therein, before the initial viewing of a user after purchasing, a best receiving direction of an antenna for each channel in which a TV broadcast of the each channel can be best received. The automatic scanning function can also be referred to as all-channel omni-directional scanning function. According to the automatic scanning function, a TV broadcast receiver sends control signals to a multi-directional antenna connected to the TV broadcast receiver so as to sequentially change or scan an active receiving direction of the antenna among the sixteen receiving directions (omni-directional scanning) for each channel, and to detect which one of the sixteen receiving directions gives best receiving condition for each channel, whereby the TV broadcast receiver automatically detects and registers best receiving directions for all the channels (all-channel scanning). By providing a TV broadcast receiver with the automatic scanning function, it becomes possible to significantly reduce labor and time for a user to make channel registration after purchasing.
For performing the automatic scanning function to determine which one of the receiving directions of the multi-directional antenna gives best receiving condition (such receiving direction being hereafter referred to as best receiving direction) for each channel, a TV broadcast receiver measures both intensity and bit error rate of a received TV broadcast signal in the case of a digital TV broadcast, while measuring only intensity of a received TV broadcast signal in the case of an analog TV broadcast. In the case of the digital TV broadcast, the best receiving direction of the antenna automatically determined by the TV broadcast receiver agrees well with that determined by a human eye, viewing an actually received image of the TV broadcast. This is because the TV broadcast receiver, operating as a digital TV broadcast receiver, makes the determination on the basis of both the intensity and bit error rate. However, in the case of the analog TV broadcast, the best receiving direction of the antenna determined by the TV broadcast receiver does not always agree with that determined by the human eye, because the TV broadcast receiver, operating as an analog TV broadcast receiver, makes the determination on the basis of only the intensity. This will be described in more detail below.
In the case of the analog TV broadcast, defects appearing on received images can be classified into noise and ghost. If the received images are determined on the basis of only the intensity, it may occur that a receiving direction of the antenna to give significant ghost may be determined as a best receiving direction, if such receiving direction gives little noise. For a user who hates ghost more than noise, the thus determined best receiving direction may not actually be best, and may have to be prevented from being selected. In other words, another receiving direction which gives less ghost, even with more noise, may be a receiving direction for such user to select, depending on the preference of the user. However, an existing analog TV broadcast receiver determines a best receiving direction on the basis of only the intensity of a TV broadcast signal of each channel as described above, and registers such receiving direction therein for the each channel. As a result, it may occur that a user cannot view the channel in a receiving direction which the user prefers to select.
Besides, in a multi-directional antenna capable of receiving both analog and digital TV broadcasts, a technology is known which quickly sets the receiving direction or directivity of the antenna to a broadcast wave to receive (refer e.g. Japanese Laid-open Patent Publication 2004-173062). However, this technology does not reflect the preference of a user to the selection of the receiving direction of the antenna.